1. Field of the Invention
This invention relates to pneumatic actuators, especially those comprising a cylinder, piston and one or more piston rods, for oil and gas well swabs where they are used to actuate valves for opening internal valves for allowing the fluid to pass through the swabs and closing such valves due to head pressure acting on the pistons as the swabs sink into the petroleum and other liquids in the well pipe.
2. Description of Prior Art
Sealing means for pneumatic apparatus for use in oil and gas well swabs as disclosed in U.S. Pat. No. 4,070,134 have been limited to the lipseals and O-rings surrounding the pistons.